1. Field of the Invention
The invention relates to the control of processes used in the manufacture of semiconductor devices, and specifically to control the integrity of thermal processes.
2. Description of the Related Art
In the process sequence of manufacturing of a semiconductor device, annealing or heating steps are applied at various stages in the process to, for example, cure damage to a semiconductor crystal which is induced by implant processes, activate implanted or deposited dopants, or cure deposited films. Traditionally, tube-type furnaces have been utilized for such annealing, but more recently, rapid thermal process technology has been investigated to improve yields and cycle times.
Use of a rapid thermal process (RTP) reduces the thermal budget required for the integrated circuit manufacturing process. For example, RTP technology is a good choice for the growth of thin oxide used in MOS transistors. The trend toward smaller feature sizes on the wafer surface has brought along with it a decrease in the thickness of layers added to the wafer. As devices are scaled to ever-smaller dimensions, the criticality of the RTP processes increases.
Oxides as thin as 100 .ANG. or less are very difficult to control in tube furnaces due to the problem of quickly supplying and removing oxygen from the system.
However, rapid thermal processing tools are seeing an increase in their use in forming such thin oxides. RTP processing tools also have applications in silicide formation, implant annealing, shallow junction formation, thermal oxidation, and chemical vapor deposition (CVD) processes.
In all of these processes, control of the ambient gases in the rapid thermal processing tool is critical to the control and repeatability of the process. For example, certain types of implanted silicon crystals such as, for example, boron, and phosphorous, are subject to an effect known as oxidation enhanced diffusion (OED). In essence, oxidation in a silicon wafer doped with one of the aforementioned impurities is enhanced in the thermal environment, and control of ambient oxygen in the annealing process is critical to ensuring that such oxidation does not destroy the device being processed.